Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $54.85   11.323%   $61.0607   $61.06   $61.05   $61.10  
  Purchase #2 $74.39   6.578%   $79.2834   $79.28   $79.30   $79.30  
  Purchase #3 $192.89   12.296%   $216.6078   $216.61   $216.60   $216.60  
  Purchase #4 $17.55   12.142%   $19.6809   $19.68   $19.70   $19.70  
  Purchase #5 $232.83   6.140%   $247.1258   $247.13   $247.15   $247.10  
  Purchase #6 $172.52   6.271%   $183.3387   $183.34   $183.35   $183.30  
  Purchase #7 $47.87   8.433%   $51.9069   $51.91   $51.90   $51.90  
  7 purchase totals = $792.90       $859.0042   $859.01   $859.05   $859.00